The present invention relates to a position measurement system which measures the current position by employing the GPS (Global Positioning System), and to a portable terminal which utilizes this position measurement system.
In the prior art, devices have been implemented in practice which perform measurement of the current position by employing GPS. As is per se well known, this position measurement by GPS is a method by which a device (a receiver) receives GPS signals emitted from at least three satellites, and calculates its own position using these GPS signals. In concrete terms, each of the satellites emits, in its GPS signal, radio waves upon which are superimposed almanac data which is information specifying the orbit of the satellite, and ephemeris data which specifies detailed starting information for the satellite and the time instant that the signal was emitted. And the measurement of the position of the receiver is performed by a triangle intersection method, using the calculated distances from the receiver of the three satellites whose GPS signals have been received.
Furthermore, as disclosed in Japanese Laid-Open Patent Publication 2005-202397 and Japanese Patent 3,671,795 etc., a practical implementation has been made of a mobile telephone endowed with GPS functionality, this telephone being provided with a GPS reception unit which receives GPS signals emitted from the GPS satellites, and measuring its own position using these GPS signals. A typical mobile telephone endowed with GPS functionality is not actually provided with the function of itself processing the GPS signals received from the GPS satellites by its GPS reception unit so as to measure its own position; rather, it transmits the GPS signals which it has received from the GPS satellites to a center. And, using these GPS signals which have been transmitted from this mobile telephone endowed with GPS functionality, the center performs a position measurement calculation in order to determine the position of said mobile telephone endowed with GPS functionality, and then returns the result of this calculation, which is the result of positional measurement, back to said mobile telephone endowed with GPS functionality. And the mobile telephone endowed with GPS functionality acquires its own position by receiving this result of position measurement from the center. This method is generally termed the MS-Assisted mode.
Furthermore, a mobile telephone endowed with GPS functionality has also been proposed (for example, in Japanese Patent Publication 2005-528049), which is endowed with a short distance wireless communication function such as BlueTooth (a trademark) or Zigbee or the like, and which notifies its own position to some other portable terminal, for example a digital camera, with this short distance wireless communication function. By doing this the portable terminal, which itself is not endowed with any position measurement function by GPS, can also acquire its own position, and can use it. For example, in the case of a digital camera, it may take the position which it has thus acquired with this short distance wireless communication with the mobile telephone endowed with GPS functionality as the position at which it has captured an image, and may append this position in correspondence with the data for the captured image. By doing this, each captured image is associated with the location where that image was captured, and accordingly it is possible to assist the user with management of captured images.
However, such a mobile telephone endowed with GPS functionality which operates according to the MS-Assisted mode transmits the GPS signals which it has received from the satellites to the center via the mobile telephone network. Due to this, when the mobile telephone endowed with GPS functionality is positioned at a location in which it cannot connect to the mobile telephone network, i.e. is in a no-service area, it cannot transmit the GPS signals which it has received from the satellites to the center. Accordingly, with a prior art type of mobile telephone endowed with GPS functionality, there has been the problem that, when this mobile telephone is located in a no-service area, it is unable to measure its own position using GPS. Furthermore, since it is not possible for this mobile telephone endowed with GPS functionality to acquire its own position, accordingly, some other terminal which attempts to acquire its own position by short distance communication with this mobile telephone endowed with GPS functionality cannot acquire its own position either. In other words, with the structure disclosed in Japanese Patent Publication 2005-528049, when the mobile telephone endowed with GPS functionality is positioned in a no-service area, neither of the devices is able to utilize its own position which has been measured using GPS.
The objective of the present invention is to provide a position measurement system which is capable of acquiring a position measurement result using GPS, even in a state in which when a portable terminal thereof whose method of measuring its own position is the MS-Assisted mode cannot connect to a center, and moreover with which this result of position measurement can be utilized by another portable terminal; and to provide said other portable terminal which is applied in this position measurement system.